A speaker produces vibrations in a vibrating element including a diaphragm by means of an audio current for sound generation. There are various forms of diaphragms in accordance with types of speakers, of which a cone shaped diaphragm is most often used for a direct-radiating type speaker. The drive unit for vibrating the vibrating element comprises a voice coil to which the audio current is applied, a voice coil bobbin having an outer periphery around which the voice coil is wound, and a magnetic circuit in which a magnetic gap is provided for allowing an electromagnetic force to act on the voice coil. The voice coil bobbin is connected to the inner periphery of the vibrating element supported at its outer periphery by the frame, so that the vibrations caused by the action of the electromagnetic force on the voice coil are transmitted through the voice coil bobbin to the vibrating element.
FIG. 1 is an illustration (sectional view) showing the related art of a cone-type speaker described in Patent Document 1 as described below. In this related art, the outmost periphery of the diaphragm J1 is connected through an edge J2 to a frame J3. The innermost diameter portion of the diaphragm J1 is connected to a voice coil bobbin J4, and the outer periphery of the voice coil bobbin J4 is held by a damper J5 secured to the frame J3 so as to center the voice coil bobbin J4. In addition, a center cap J6 is attached to the surface of the diaphragm J1. A magnetic circuit J7 is disposed in the lower portion of the frame J3. A voice coil J8, which is wound on the lower portion of the voice coil bobbin J4, is disposed in a magnetic gap J7A in the magnetic circuit J7. Then, in this structure, the outer circumferential rim of the center cap J6 is fitted into a stepped stage J1A formed on the diaphragm J1.
Patent Document 1: Japanese Patent No. 3433342.